This application is based on Japanese Patent Application No. 2001-340872, filed on Nov. 6, 2001, the entire contents of which are incorporated herein by reference.
A) Field of the Invention
The present invention relates to a semiconductor device with fuses and its manufacture method, and more particularly to techniques regarding fuse elements used in a trimming circuit or a redundancy circuit of a semiconductor integrated circuit.
B) Description of the Related Art
A trimming circuit and a redundancy circuit are often formed in a semiconductor integrated circuit. If a fuse circuit having fuse elements is used as a trimming circuit or a redundancy circuit, a trimming process and the like can be performed during or after the manufacture of a semiconductor integrated circuit so that the characteristics of the circuit can be improved as much as possible.
Japanese Patent Laid-open Publication HEI-7-307389 discloses in FIG. 1 a circuit having a plurality of parallel connections of a serial connection of a fuse element and a MOS transistor. It discloses that a current drive ability necessary for obtaining a breakdown current for breaking down a fuse element is given by a function of the gate width W of a selection transistor:
xe2x80x83ID=xcexcCox(W/L)xc3x97(xc2xd)xc3x97(VGSxe2x88x92VY)2
where ID is a drain current of a selection transistor in a saturation region, and xcexc is a mobility of carriers. Cox is a gate capacitance of the selection transistor, W is a gate width and L is a gate length. VGS is a gate-source voltage and VY is a threshold voltage.
If the value ID of a saturation drain current necessary for breaking down a fuse element is known, the gate width W (size) of the transistor capable of breaking down the fuse element can be estimated from the above-described equation. This analysis adopts the assumption that the saturation current of a MOS transistor is used for breaking down a fuse.
In order to melt and break down a fuse element, it is necessary to flow current through the fuse element and heat it to a temperature over the melting point thereof. For example, if single crystal silicon or polysilicon is used as the material of a fuse element, a relatively large current is required because the melting point of silicon is as high as about 1420xc2x0 C. It is therefore necessary to make large the size of a selection transistor, which hinders high integration of device elements. According to the above-described Publication, a bipolar transistor having a high current drive ability is used as a selection transistor to obtain a large current.
Most of recent integrated circuits are MOS type ICs using MOS FETs as fundamental device elements. If a bipolar transistor is required to be formed in a MOS type IC, the element structure becomes complicated and additional processes are necessary.
An object of this invention is to reduce an area occupied by a fuse circuit having a fuse element and a selection transistor and fabricated in a MOS IC, by using a MOSFET as the selection transistor and reducing the area occupied by the selection transistor.
According to one aspect of the present invention, there is provided a semiconductor device comprising: a fuse element capable of being electrically broken down by flowing current therethrough, a first voltage being applied to one end of the fuse element; and a MOS type transistor having source, gate and drain terminals and a connection point between the other end of the fuse element and one of the source and drain terminals, a second voltage lower than the first voltage being applied to the other of the source and drain terminals, wherein: the first and second voltages, characteristics of the MOS type transistor and a resistance value of the fuse element are selected so that the fuse element can be broken down when a predetermined program voltage is applied to the gate terminal; and the resistance value of the fuse element is set to such a value as a voltage difference between a voltage at the connection point and the second voltage is lower than a drain voltage of the MOS type transistor at which a drain current starts saturating, when the program voltage is applied to the gate terminal
According to another aspect of the present invention, there is provided a semiconductor device comprising: a fuse element capable of being electrically broken down by flowing current therethrough, a first voltage being applied to one end of the fuse element; and a MOS type transistor having source, gate and drain terminals and a connection point between the other end of the fuse element and one of the source and drain terminals, a second voltage lower than the first voltage being applied to the other of the source and drain terminals, wherein: the first and second voltages, characteristics of the MOS type transistor and a resistance value of the fuse element are selected so that the fuse element can be broken down when a predetermined program voltage is applied to the gate terminal; and the resistance value of the fuse element is further set to such a value as a minimum power capable of breaking down the fuse element is not smaller than 90% of a maximum consumption power of the fuse element calculated from current-voltage characteristics of the MOS type transistor.
According to another aspect of the present invention, there is provided a semiconductor device comprising: a fuse element capable of being electrically broken down by flowing current therethrough, a first voltage being applied to one end of the fuse element; and a MOS type transistor having source, gate and drain terminals and a connection point between the other end of the fuse element and one of the source and drain terminals, a second voltage lower than the first voltage being applied to the other of the source and drain terminals, wherein: the first and second voltages, characteristics of the MOS type transistor and a resistance value of the fuse element are selected so that the fuse element can be broken down when a predetermined program voltage is applied to the gate terminal; and the resistance value of the fuse element is further set to such a value as a breakdown current of the fuse element is in a range from 80% to 98% of a saturation drain current of the MOS type transistor.
A power supplied to the semiconductor device can be used efficiently for breaking down the fuse element.
According to a further aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising steps of: forming on a substrate a serial connection of a fuse element and a MOS type transistor, the fuse element being capable of being electrically broken down by flowing current therethrough, and the MOS type transistor having source, gate and drain terminals and a connection point between one end of the fuse element and one of the source and drain terminals; and applying a voltage higher than a drain voltage of the MOS type transistor at which a drain current starts saturation, between another end of the fuse element and the other of the source and drain terminals, applying a predetermined program voltage to the gate terminal, and breaking down the fuse element by setting a voltage at the connection point between the fuse element and the MOS type transistor to a voltage lower than a drain voltage of the MOS type transistor in a saturation region in which a drain current saturates.
According to another aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising steps of: forming on a substrate a serial connection of a fuse element and a MOS type transistor, the fuse element being capable of being electrically broken down by flowing current therethrough, a first voltage being applied to one end of the fuse element, the MOS type transistor having source, gate and drain terminals and a connection point between one end of the fuse element and one of the source and drain terminals, and a second voltage lower than the first voltage being applied to the other of the source and drain terminals; and applying a voltage higher than a drain voltage of the MOS type transistor at which a drain current starts saturation, between the other end of the fuse element and the other of the source and drain terminals, applying a predetermined program voltage to the gate terminal, and breaking down the fuse element by setting a voltage at the connection point of the MOS type transistor in a voltage range in which a consumption power of the fuse element is not smaller than 90% of a maximum consumption power of the fuse element calculated from current-voltage characteristics of the MOS type transistor.
According to another aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising steps of: forming on a substrate a serial connection of a fuse element and a MOS type transistor, the fuse element being capable of being electrically broken down by flowing current therethrough, a first voltage being applied to one end of the fuse element, the MOS type transistor having source, gate and drain terminals and a connection point between one end of the fuse element and one of the source and drain terminals, and a second voltage lower than the first voltage being applied to the other of the source and drain terminals; and applying a voltage higher than a drain voltage of the MOS type transistor at which a drain current starts saturation, between the other end of the fuse element and the other of the source and drain terminals, applying a predetermined program voltage to the gate terminal, and breaking down the fuse element by setting a voltage at the connection point between the fuse element and the MOS type transistor in a voltage range in which 80% to 98% of a saturation current of the MOS type transistor flows.
As above, in the fuse circuit made of a serial connection of a fuse element and a selection transistor, the power supplied to the fuse circuit can be used efficiently for breaking down the fuse element. It is therefore possible to reduce the area occupied by the selection transistor.